Heat recovery system and method

ABSTRACT

The present invention relates to a heat recovery system and method for recovering heat for heating water to a predetermined temperature. There is disclosed a heat recovery system comprising an Organic Rankine Cycle (ORC) system and a heat pump system, wherein the ORC system is operatively coupled to the heat pump system via coupling means. Heat that is recovered from the heat recovery system is used for heating water to a predetermined temperature.

FIELD OF INVENTION

The present invention relates to a heat recovery system and method and in particular, but not exclusively, to a heat recovery system and method for recovering heat for heating water or other liquids to a predetermined temperature.

BACKGROUND TO THE INVENTION

The following discussion of the background to the invention is intended to facilitate an understanding of the present invention. However, it should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was published, known or part of the common general knowledge in any jurisdiction as at the priority date of the application.

A heat pump is a device that provides heat energy from a heat source to a destination typically known as a “heat sink”. A heat pump is designed to move thermal energy opposite to the direction of spontaneous heat flow by absorbing heat from a cold area and releasing it to a warmer one. A heat pump uses some amount of external high grade energy, such as electricity, to carry out the work of transferring energy from the heat source to the heat sink, where heat may be recovered for utilization.

The two main types of heat pumps are, namely, compression heat pumps and absorption heat pumps. Compression heat pumps are typically cooled by ambient air or water, and driven by an electric power source. Absorption heat pumps are typically driven by thermal heat fueled by natural gas or liquefied petroleum gas, for example. Other types of fuels to generate thermal heat may be in the form of flue gas, steam and/or hot water.

Although heat pumps may be useful for recovering waste heat, the need for electrical energy or energy from burnable fuels to drive heat pumps detracts from the overall efficiency of such systems.

Therefore, the present invention seeks to provide a heat recovery system and method that overcomes, or at least alleviates, the above-mentioned problems.

SUMMARY OF THE INVENTION

In particular, but not exclusively, the invention seeks to provide a heat recovery system and method for recovering heat for heating water to a predetermined temperature.

In accordance with a first aspect of the present invention, there is provided a heat recovery system comprising an Organic Rankine Cycle (ORC) system comprising an evaporator, an expander, a condenser and a pump connected in a closed loop; a heat pump system comprising an evaporator, a compressor, a condenser and a control valve connected in a closed loop; and coupling means, wherein the ORC system is operatively coupled to the heat pump system via the coupling means and wherein the condenser of the ORC system and the condenser of the heat pump system is a common condenser to both the ORC system and the heat pump system for recovering heat.

Preferably, the heat recovered is for heating water to a predetermined temperature. The predetermined temperature is ideally in a range of about 50° C. to about 80° C. Preferably, the expander of the ORC system is operatively coupled to the compressor of the heat pump system via the coupling means. Preferably the coupling means comprises a shaft and a clutch. The clutch is preferably used for coupling and decoupling the expander of the ORC system to the compressor of the heat pump system.

Preferably, the expander of the ORC system is a screw-type expander.

Preferably, the compressor of the heat pump system is a screw-type compressor.

Preferably, the heat recovery system further comprises a work fluid.

Preferably, the work fluid comprises a first organic fluid and a second organic fluid.

Preferably, the work fluid comprises an azeotropic mixture of a pentafluorobutane and a perfluoropolyether.

Preferably, the ORC system further comprises a heat source coupled to the evaporator of the ORC system.

Preferably, the heat pump system further comprises a heat source coupled to the evaporator of the heat pump system. The heat source is preferably generated based on ambient temperature of water and/or waste heat.

Preferably, the ambient temperature of water as heat source is between 30° C. to 40° C.

Preferably, the temperature of waste heat as heat source is between 130° C. to about 150° C.

In accordance with a second aspect of the invention there comprises a method for heat recovery comprising the following steps: connecting an Organic Rankine Cycle (ORC) system comprising an evaporator, an expander, a condenser and a pump in a closed loop; connecting a heat pump system comprising an evaporator, a compressor, a condenser and a control valve in a closed loop; and coupling the ORC system to the heat pump system via coupling means; wherein the condenser of the ORC system and the condenser of the heat pump system is a common condenser to both the ORC system and the heat pump system for recovering heat.

Other aspects and features of the present invention will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described, by way of illustrative example only, with reference to the accompanying drawings, of which:

FIG. 1 shows a heat recovery system in accordance with an embodiment of the present invention; and

FIG. 2 shows a heat recovery system with only the Organic Rankine Cycle (ORC) system in operation in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, the same reference numbers refer to same or similar parts. Different embodiments of similar parts are marked with primes.

FIG. 1 shows a heat recovery system 10 in accordance with an embodiment of the present invention. The heat recovery system 10 is driven by waste heat as opposed to electric power and is used for, but not exclusively, recovering heat for heating a liquid (for example water) to a predetermined temperature. Surprisingly and advantageously, the heat recovered by the heat recovery system 10 can heat water to a relatively higher temperature, in the range of about 50° C. to about 80° C., by utilizing ambient temperature of water. Alternatively, waste heat may be used as heat source, having a temperature range of between 130° C. to 150° C.

The heat recovery system 10 comprises an Organic Rankine Cycle (ORC) system 12, which comprises a plurality of heat exchangers. The plurality of heat exchangers may include an evaporator 14, an expander 16, a condenser 18 and a pump 20, typically in the form of a hydraulic diaphragm metering pump or the like, connected in a closed loop via respective work fluid inlets and outlets typically in the form of pipes or conduits described hereinafter. The ORC system 12 further comprises a heat source 22 that is coupled to the evaporator 14. The heat source 22 can be from waste heat generated with a temperature range of about 130° C. to about 150° C.

The evaporator 14 is connected to the expander 16 via an outlet 24 of evaporator 14 and an inlet 26 of the expander 16. The expander 16 is connected to the condenser 18 via an outlet 28 of the expander 16 and an inlet 30 of the condenser 18. The condenser 18 is connected to the pump 20 via an outlet 32 of the condenser 18 and an inlet 34 of the pump 20. The pump 20 is then connected to the evaporator 14 via an outlet 36 of the pump 20 and an inlet 38 of the evaporator 14 forming a closed loop.

The heat recovery system 10 also comprises a heat pump system 40, which comprises an evaporator 42, a compressor 44, a condenser which is the common condenser 18 to both the ORC system and the heat pump system 40 and a control valve 46. The control valve 46 may typically be an expansion valve and more preferably a throttle expansion valve connected in a closed loop via respective work fluid inlets and outlets typically in the form of pipes or conduits described hereinafter. The heat pump system 40 further comprises a heat source 48 which is coupled to the evaporator 42. The heat source 48 can be from waste heat, ambient temperature of water or the like, and has a temperature range of about 30° C. to about 40° C.

The evaporator 42 is connected to the compressor 44 via an outlet 50 of evaporator 42 and an inlet 52 of the compressor 44. The compressor 44 is connected to the condenser 18 via an outlet 54 of the compressor 44 and the inlet 30 of the condenser 18. The condenser 18 is connected to the control valve 46 via the outlet 32 of the condenser 18 and an inlet 56 of the control valve 46. The control valve 46 is then connected to the evaporator 42 via an outlet 58 of the control valve 46 and an inlet 60 of the evaporator 42 forming a closed loop.

The common condenser 18 or condenser 18 comprises a heat output 62 whereby recovered heat obtained is used for, but not exclusively, heating water to a predetermined temperature. Preferably, the predetermined temperature is in the range of about 50° C. to about 80° C.

The heat recovery system 10 also comprises coupling means 64 in which the ORC system 12 is operatively coupled to the heat pump system 40 via the coupling means 64. In particular, the expander 16 of the ORC system 12 is operatively coupled to the compressor 44 of the heat pump system 40 via the coupling means 64. Preferably, the expander 16 of the ORC system 12 is a screw-type expander, and the compressor 44 of the heat pump system 40 is a screw-type compressor. It is advantageous for the expander 16 and the compressor 44 to be of the screw-type because in slightly wet operations, no lubricant(s) is needed.

In the described embodiment, the coupling means 64 comprises a shaft, typically in the form of a turbine shaft, and a clutch (not shown) for coupling and decoupling the expander 16 of the ORC system 12 to the compressor 44 of the heat pump system 40. The clutch may be a freewheel clutch, and preferably an electromagnetic clutch for decoupling the expander 16.

The unique combination of the ORC system 12 operatively coupled to the heat pump system 40 forming the heat recovery system 10 provides several advantages. The heat recovery system 10 is advantageous as the compressor 44 of the heat pump system 40 is directly drive by the turbine shaft, hence, there is no need to for an electric generator in the ORC system 12 nor an electric motor in the heat pump system 40. The heat recovery system 10 is able to utilize waste heat not just for the recovery of heat but also for driving the system 10. The only exception of the system 10 which requires electric power consumption is the operation of the pump 20 of the ORC system 12. However, only a very small amount of electric power is required to operate the pump 20, which is negligible.

The condenser 18 which is common to both the ORC system 12 and the heat pump system 40 is advantageous as the heat recovered via the heat output 62 is from both the ORC system 12 and the heat pump system 40. Such recovered heat is capable of heating water to a higher temperature in the range of about 50° C. to about 80° C., by utilizing a substantially lower ambient temperature of water of about 30° C. to about 40° C. and/or waste heat having a temperature range from 130° C. to about 150° C. of the heat sources 48,22.

When the heat recovery system 10 is in operation, work fluid is being circulated in the closed loop of the ORC system 12 and the closed loop of the heat pump system 40.

Heat such as waste heat from the heat source 22 of the ORC system 12 is supplied to the evaporator 14 of the ORC system 12 for utilization. The waste heat is used by the evaporator 14 to change the state of the work fluid from a liquid state to high pressure vapour state. The pressurized vapour is circulated from the evaporator 14 and forced through the expander 16 via the outlet 24 of the evaporator 14 and the inlet 26 of the expander 16. The expansion of the pressurized vapour by the expander 16 produces power, which is used to drive the compressor 44 of the heat pump system 40 via the shaft. The vapour then exits the expander 16 via the outlet 28 of the expander 16 as a low pressure vapour and flows to the condenser 18 via the inlet 30 of the condenser 18. The low pressure vapour is cooled and condensed back into a liquid state in the condenser 18. The liquid state work fluid then leaves the condenser 18 via the outlet 32 of the condenser 18 and is pumped by the pump 20 to a higher pressure. The higher pressure work fluid is returned to the evaporator 14 via the outlet 36 of the pump 20 and the inlet 38 of the evaporator 14 to repeat the cycle as described above.

Simultaneous to the cycle described above for the ORC system 12, work fluid is also being circulated in the closed loop of the heat pump system 40. Heat such as from ambient temperature of water from the heat source 48 of the heat pump system 40 is supplied to the evaporator 42 of the heat pump system 40 for utilization. The waste heat is used by the evaporator 42 to change the state of the work fluid from a liquid state to a vapour state. The vapour leaves the evaporator 42 via the outlet 50 of the evaporator 42 and enters the compressor 44 in a low pressure, low temperature gaseous state via the inlet 52 of the compressor 44. The compressor 44, being driven by the expander 16 of the ORC system 12 via the shaft, compresses the vapour to a high pressure and temperature gaseous state. The high pressure and temperature vapour then leaves the compressor 44 via the outlet 54 of the compressor 44 and enters the condenser 18 via the inlet 30 of the condenser 18. In the condenser 18, the vapour is precipitated into a high pressure liquid by the transfer of heat to the heat output 62. The high pressure liquid then leaves the condenser 18 via the outlet 32 of the condenser 18 and enters the control valve 46 via the inlet 56 of the control valve 46. The high pressure liquid enters the control valve 46 and the control valve 46 controls the amount of work fluid being circulated to the evaporator 42 by allowing a portion of the work fluid to enter the evaporator 42. It is important for the control valve 46 to control or limit the flow of the work fluid to the evaporator 42 so as to keep the pressure low and hence allow expansion of the work fluid back into a gaseous state. The work fluid, a mixture of liquid state and gaseous state, leaves the control valve 46 via the outlet 58 of the control valve 46 and enters the evaporator 42 via the inlet 60 of the evaporator 42 to repeat the cycle as described above.

The work fluid used in the described embodiment is an organic fluid comprising a first organic fluid such as pentafluorobutane and a second organic fluid such as perfluoropolyether. The work fluid selected for use preferably fulfills the following criteria:—

-   -   1. non-toxic     -   2. non-flammable     -   3. non-corrosive and fouling resistant     -   4. material compatibility and suitable fluid stability limits     -   5. high latent heat and high density     -   6. low environmental impact     -   7. acceptable pressure range for screw expanders     -   8. safety

In particular, SES36 is a suitable work fluid for use. SES36 is an azeotropic mixture of 365mfc (1,1,1,3,3 pentafluorobutane) and PFPE (perfluoropolyether). It is advantageous to use SES36 as a work fluid as it also has a lubricating property. Alternatively, other types of work fluid which fulfills the above criteria and/or have properties similar to SES36 may also be used.

In an example, the heat recovery system 10 is being operated based on the following specifications listed in Table 1 as follows:

Hot water supply capacity 101.81 kW Hot water temperature 55-60° C. Heat input to evaporator of ORC system 50 kW COPh 2.04 ORC system Turbine efficiency 0.75 Pump efficiency 0.8 Cycle efficiency 0.1 Turbine output 5.26 kW Pump input 0.27 kW Condenser 45.02 kw Heat pump system Compressor efficiency 0.75 Wet % in compression 5.8% Compressor input 5.07 kW Evaporator 65.19 kW Condenser 56.79 kW COP 12.85 Work fluid (Refrigerant) SES 36

In this example, the heat input from the heat source 22 to the evaporator 14 of the ORC system 12 is about 50 kW. The work fluid that leaves the evaporator 14 has a pressure of 12.05 bar, a temperature of 130.0° C., a specific enthalpy of 441.99 kJ/kg, and the flow rate of the work fluid, i.e. SES36 has a flow rate of M=281.8 g/sec. After the work fluid enters the expander 16, the work fluid that leaves the expander 16 has a pressure of 2.2 bar, a temperature of 96.58° C., and a specific enthalpy of 423.34 kJ/kg, and enters the condenser 18. After the work fluid leaves the condenser 18, the work fluid has a pressure of 2.2 bar, a temperature of 60.0° C., and a specific enthalpy of 263.62 kJ/kg. The work fluid then enters the pump 20 and is pumped back to the evaporator 14. The work fluid that leaves the pump 20 has a pressure of 12.05 bar, a temperature of 60.89° C., and a specific enthalpy of 264.59 kJ/kg.

In this same example, the heat input from the heat source 48 to the evaporator 42 of the heat pump system 40 is about 65.19 kW. The work fluid in the heat pump system 40 that leaves the evaporator 42 has a pressure of 1.17 bar, a temperature of 40.0° C., a specific enthalpy of 369.60 kJ/kg, and a mass flow rate of M=488 g/sec. After the work fluid enters the compressor 44, the work fluid that leaves the compressor 44 has a pressure of 2.2 bar, a temperature of 60.0° C., and a specific enthalpy of 379.99 kJ/kg, and enters the condenser 18. After the work fluid leaves the condenser 18, the work fluid has a pressure of 2.2 bar, a temperature of 60.0° C., and a specific enthalpy of 263.62 kJ/kg. The work fluid then enters the control valve 46 and is circulated back to the evaporator 42. The work fluid that leaves the control valve 46 has a pressure of 0.99 bar, a temperature of 35.0° C., and a specific enthalpy of 236.03 kJ/kg.

FIG. 2 shows a heat recovery system 10′ with only an ORC system 12′ in operation in accordance with another embodiment of the present invention. The ORC system 12′ similarly comprises an evaporator 14′, an expander 16′, a condenser 18′ and a pump 20′, typically in the form of an absorption pump or the like, connected in a closed loop via respective work fluid inlets and outlets typically in the form of pipes or conduits described hereinafter. The ORC system 12′ further comprises a heat source 22′ which is coupled to the evaporator 14′. The heat source 22′ can be from waste heat having a temperature range of between about 120° C. to about 150° C.

The evaporator 14′ is connected to the expander 16′ via an outlet 24′ of evaporator 14′ and an inlet 26′ of the expander 16′. The expander 16′ is connected to the condenser 18′ via an outlet 28′ of the expander 16′ and an inlet 30′ of the condenser 18′. The condenser 18′ is connected to the pump 20′ via an outlet 32′ of the condenser 18′ and an inlet 34′ of the pump 20′. The pump 20′ is then connected to the evaporator 14′ via an outlet 36′ of the pump 20′ and an inlet 38′ of the evaporator 14′ forming a closed loop.

The common condenser 18′ or condenser 18′ similarly comprises a heat output 62′ whereby recovered heat obtained is used for, but not exclusively, heating water to a predetermined temperature. Preferably, the predetermined temperature is in the range of about 50° C. to about 80° C.

The ORC system 12′ further comprises a generator 66 for generating electric power and coupling means 68 for operatively coupling the expander 16′ to the generator 66. The coupling means 68 comprises a shaft, typically in the form of a turbine shaft, and a clutch (not shown) for coupling and decoupling the expander 16′ of the ORC system 12′ to the generator 66. In this described embodiment, the heat recovery system 10′ is able to recover heat for heating water to a predetermined temperature as well as to generate electric power via the generator 66.

In an example, the heat recovery system 10′ is being operated based on the following specifications listed in Table 2 as follows:

Hot water supply capacity 45.55 kW Hot water temperature 80.0° C. Heat input to evaporator of ORC system 50 kW COPh = 45.55/50 0.911 ORC system Turbine efficiency 0.75 Pump efficiency 0.8 Cycle efficiency 0.09 Turbine Electric power output 4.88 kW Pump input 0.3 kW Condenser 45.55 kw Heat pump system — Compressor efficiency — Compressor input — Evaporator — Condenser — COP — Work fluid (Refrigerant) SES 36

In this example, the heat input from the heat source 22′ to the evaporator 14′ of the ORC system 12′ is about 50 kW. The work fluid that leaves the evaporator 14′ has a pressure of 17.62 bar, a temperature of 150.0° C., a specific enthalpy of 455.48 kJ/kg, and a mass flow rate of M=299.2 g/sec. After the work fluid enters the expander 16′, the work fluid that leaves the expander 16′ has a pressure of 3.84 bar, a temperature of 80.0° C., and a specific enthalpy of 439.18 kJ/kg, and enters the condenser 18′. After the work fluid leaves the condenser 18′, the work fluid has a pressure of 3.84 bar, a temperature of 80.0° C., and a specific enthalpy of 286.93 kJ/kg. The work fluid then enters the pump 20′ and is pumped back to the evaporator 14′. The work fluid that leaves the pump 20′ has a pressure of 17.62 bar, a temperature of 81.27° C., and a specific enthalpy of 288.35 kJ/kg.

Although the foregoing invention has been described in some detail by way of illustration and example, and with regard to one or more embodiments, for the purposes of clarity of understanding, it is readily apparent to those of ordinary skill in the art in light of the teachings of this invention that certain changes, variations and modifications may be made thereto without departing from the spirit or scope of the invention as described in the appended claims.

It would be further appreciated that although the invention covers individual embodiments, it also includes combinations of the embodiments discussed. For example, the features described in one embodiment is not being mutually exclusive to a feature described in another embodiment, and may be combined to form yet further embodiments of the invention. 

1. A heat recovery system comprising: an Organic Rankine Cycle (ORC) system comprising an evaporator, an expander, a condenser and a pump connected in a closed loop; a heat pump system comprising an evaporator, a compressor, a condenser and a control valve connected in a closed loop; and coupling means, wherein the ORC system is operatively coupled to the heat pump system via the coupling means and wherein the condenser of the ORC system and the condenser of the heat pump system is a common condenser to both the ORC system and the heat pump system for recovering heat; the common condenser comprises a heat output operable to recover waste heat; and wherein the coupling means comprises a shaft and a clutch operatively coupling the expander of the ORC system to the compressor of the heat pump system.
 2. The heat recovery system according to claim 1, wherein the clutch is for coupling and decoupling the expander of the ORC system to the compressor of the heat pump system.
 3. The heat recovery system according to claim 1, wherein the expander of the ORC system is a screw-type expander.
 4. The heat recovery system according to claim 1, wherein the compressor of the heat pump system is a screw-type compressor.
 5. The heat recovery system according to claim 1, further comprising a work fluid.
 6. The heat recovery system according to claim 5, wherein the work fluid comprises a first organic fluid and a second organic fluid.
 7. The heat recovery system according to claim 5, wherein the work fluid comprises an azeotropic mixture of a pentafluorobutane and a perfluoropolyether.
 8. The heat recovery system according to claim 1, wherein the ORC system further comprises a heat source coupled to the evaporator of the ORC system.
 9. The heat recovery system according to claim 1, wherein the heat pump system further comprises a heat source coupled to the evaporator of the heat pump system.
 10. The heat recovery system according to claim 8, wherein the heat source is from ambient temperature of water and/or waste heat.
 11. The heat recovery system according to claim 8, wherein the heat source is of a temperature range of about 30° C. to about 40° C., and about 130° C. to about 150° C. waste heat.
 12. The heat recovery system according to claim 1, wherein the heat recovered is for heating water to a predetermined temperature.
 13. The heat recovery system according to claim 12, wherein the predetermined temperature is in a range of about 50° C. to about 80° C.
 14. The heat recovery system according to claim 3, wherein in operation the wet percentage in compression is about 5.6%.
 15. A method for heat recovery comprising the following steps: connecting an Organic Rankine Cycle (ORC) system comprising an evaporator, an expander, a condenser and a pump in a closed loop; connecting a heat pump system comprising an evaporator, a compressor, a condenser and a control valve in a closed loop; and coupling the ORC system to the heat pump system via coupling means; wherein the condenser of the ORC system and the condenser of the heat pump system is a common condenser to both the ORC system and the heat pump system for recovering heat; and the common condenser comprises a heat output operable to recover waste heat; wherein the coupling means comprises a shaft and a clutch operatively coupling the expander of the ORC system to the compressor of the heat pump system. 